In order to identify whether there are differences depending on the latitude within Sweden, children will be recruited both from northern Sweden (Umeå) and from southern Sweden (Malmo). As it is unclear what levels of the serological marker 25 (OH) D that affect the health of children, different markers of health will be examined before and after the intervention. Children aged 5-8 years, 50% fair-skin 50 % darker skin, in northern Sweden (Umeå) and southern Sweden (Malmö) will be included in a longitudinal, randomized trial. The children are first examined in November-December and randomized to a vitamin D supplement of either 10 or 25 g per day, to be used for three months. At the follow up in February-March all examinations will be repeated.